Portable medical devices are useful for patients that have conditions that must be monitored on a continuous or frequent basis. For example, diabetics are usually required to modify and monitor their daily lifestyle to keep their body in balance, in particular, their blood glucose (BG) levels. Individuals with Type 1 diabetes and some individuals with Type 2 diabetes use insulin to control their BG levels. To do so, diabetics routinely keep strict schedules, including ingesting timely nutritious meals, partaking in exercise, monitoring BG levels daily, and adjusting and administering insulin dosages accordingly.
The prior art includes a number of fluid infusion devices and insulin pump systems that are designed to deliver accurate and measured doses of insulin via infusion sets (an infusion set delivers the insulin through a small diameter tube that terminates at, e.g., a cannula inserted under the patient's skin) In lieu of a traditional syringe, the patient can simply activate the insulin pump to administer an insulin bolus as needed, for example, in response to the patient's current BG level.
A typical infusion pump includes a housing, which encloses a pump drive system, a fluid containment assembly, an electronics system, and a power supply. The pump drive system typically includes a small motor (DC, stepper, solenoid, or other varieties) and drive train components such as gears, screws, and levers that convert rotational motor motion to a translational displacement of a piston in a reservoir, which may be in the form of a user-filled syringe or a pre-filled syringe. The fluid containment assembly typically includes the reservoir with the piston, tubing, and a catheter or infusion set to create a fluid path for carrying medication from the reservoir to the body of a user. The electronics system regulates power from the power supply to the motor. The electronics system may include programmable controls to operate the motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended period.
The presence of air bubbles in a fluid syringe is undesirable for various reasons. Accordingly, air inside of user-filled syringes is usually expelled before the syringe is used. Moreover, air might be introduced into a pre-filled syringe during the filling and sealing processes. Therefore, various manufacturing techniques are implemented in an attempt to remove air from pre-filled syringes before sealing and/or to minimize the amount of air that gets introduced into the fluid. In this regard, conventional approaches often rely on vacuum filling and/or vacuum stoppering to remove or reduce the amount of air that gets trapped in the pre-filled syringes. Such techniques, however, involve specialized equipment, require additional handling of the product, and result in lower throughput.
Moreover, the piston seal of a pre-filled syringe could be affected by the medication fluid, especially during an extended shelf life. For example, the piston seal might be compressed or flattened against the reservoir wall such that the amount of force required to actuate the piston increases relative to some nominal amount. Increased actuation force may be undesirable, especially in portable devices that rely on battery power. In addition, the sealing characteristics of a piston seal could be degraded by the medication fluid if the pre-filled syringe is not used within an acceptable time period after manufacture.
Accordingly, it is desirable to have a different methodology for handling gas trapped inside of a fluid syringe. In addition, it is desirable to have a syringe piston design and a related syringe piston that can be manipulated to manage the presence of gas inside of the fluid chamber. Furthermore, it is desirable to have improved piston seal configurations that are suitable for use with pre-filled syringes and reservoirs.